FIG. 9 shows a construction of the vicinity of a probe head of a prior art microwave band probing apparatus for testing a semiconductor device operating at a microwave band in on-wafer state. In FIG. 9, reference numeral 20 designates an approximately U-shaped top plate. Positioning adjustment mechanisms 21 respectively called positioners are disposed on the top plate 20. Members 22 respectively called risers are fixed to the positioners 21, and arm members 23 respectively called zero degree arms are provided at the top ends of the risers 22. X-axis micrometer heads 24 are provided for adjusting the positions in the x-axis direction of the positioners 21. Y-axis micrometer heads 25 are provided for adjusting the positions in y-axis direction of the positioners 21. Z-axis micrometer heads 26 are provided for adjusting the positions in the z-axis direction of the positioners 21. Reference numeral 4 designates probe heads fixed to the top ends of the arm members 23.
FIGS. 10(a), and 10(b) are a perspective view and a partial cross-sectional view, respectively, showing the vicinity of the probe head 4 of the microwave band probing apparatus in a state where the apparatus is used. In the figures, reference numeral 3 designates a probe stage comprising a conductor such as metal serving as a plate for mounting a wafer 2. The wafer 2 comprises a compound semiconductor such as gallium arsenide on which a circuit 2a comprising an active element and a passive element (hereinafter referred to as "microwave monolithic integrated circuit", i.e., "MMIC") is provided. Reference numeral 4 designate RF probe heads having coplanar lines produced by evaporation or the like of metal, for example, Au on a dielectric material layer comprising such as sapphire. RF input and output electrode pads 5a of the MMIC 2a are produced by evaporation or the like of metal, for example, Au on the wafer 2. Reference numeral 27 designates coaxial cables for applying a signal to the coplanar lines of the RF probe heads 4.
FIG. 10(c) is a plan view illustrating a detail construction of the RF probe head 4, and probes 41a and 41b comprising coplanar lines are provided on one side surface of the dielectric layer 40 comprising sapphire. These probes 41a and 4lb are electrically connected to the coaxial cable 27 by wirings 42, whereby a prescribed test signal (microwave signal) is supplied to the probe 41a and the ground voltage is supplied to the probes 41b. The probes 41b are in contact with a grounding electrode pad 5b at the surface of the MMIC 2a (FIG. 10(d)).
FIG. 11 shows a perspective view illustrating a state where the MMIC 2a is mounted in a package. In the figure, reference numeral 13 designates a lid for the package comprising a metal. A package body 12 comprises a conductive layer. A cavity wall 12a is provided for containing the MMIC 2a. A microstrip line 14 is produced by evaporating a metal such as Au, 14b on a dielectric material layer 14a comprising sapphire on the package body 12. Reference numeral 15 designate wires each comprising a conductive material for connecting the metal 14b of the microstrip line 14 and the electrode pad of the MMIC 2a.
FIGS. 12(a) 12(b) are a partial cross-sectional view and a plan view, respectively, showing the vicinity of an RF probe head of a microwave probing apparatus employing a TAB tape for the probe needle. In the figures, reference numeral 9 designates a dielectric material layer comprising a polyimide TAB tape. A metal layer 8 serving as a ground layer is produced at the entire surface of one side of the dielectric material layer 9. Signal lines 10 comprising metal such as Au are produced on the other side surface of the dielectric material layer 9 by evaporation, and contact electrodes 10a are produced at the top ends thereof. A microstrip line is constituted by the dielectric material layer 9, the metal layer 8 and the signal lines 10. Reference numeral 9a designates an aperture produced at the dielectric material layer 9.
A description is given of the probing methods employing these probing apparatus.
First of all, when the probing apparatus of the structure of FIG. 10(a) is employed, the wafer 2 mounted on the probe stage 3 is fixed by a vacuum mechanism (not shown) of the probe stage 3, and the RF probe heads 4 are brought into contact with the RF I/O electrode pads 5a of the MMIC 2a produced on the wafer 2. A microwave signal that is input from one probe head 4 in this state is amplified, reflected, and attenuated at the MMIC 2a, and is output from the other RF probe head 4. By measuring the input signal, output signal and reflected signal, microwave characteristics such as power, noise, or the like, of the MMIC 2a are obtained. A rear surface metal 2b is produced on the entire rear surface of the wafer 2 as shown in FIG. 10(d), and this rear surface metal 2b and the ground electrode pad 5b are connected via a via-hole 2c, whereby when the transmission line of the MMIC 2a is a microstrip line, the ground plane thereof is the probe stage 3, i.e., the wafer rear surface.
A description is given of the method for measuring the microwave characteristics of the MMIC which is mounted on a package. In FIG. 11, a microwave signal is transmitted through the input side microstrip line 14a and the wiring 15 and input to the MMIC 2a on the conductive layer 12. The microwave signal which is amplified or attenuated here is transmitted through the output side microstrip line 14a and output therefrom. By measuring the input signal, output signal, and reflected signal or the like, microwave characteristics such as power, noise, or the like, of the MMIC 2a are obtained. The ground plane of the MMIC 2a then is the conductive layer 12, the cavity wall 12a and the lid 13 of the package.
A description is given of the probing method using the TAB tape of FIG. 12(a). By contact the RF I/O electrode pads 5a to the wafer 2 and the contact electrodes 10a produced at the top ends of the signal lines 10 of the TAB tape to each other, a microwave signal is transmitted on the microstrip line comprising the ground layer 8, the dielectric material layer 9 and the signal lines 10, and after amplification or attenuation by the MMIC 2a, it is transmitted through the other TAB tape microstrip line and output. By measuring the input signal, output signal, and reflected signal or the like, microwave characteristics such as power, noise or the like, of the MMIC 2a are obtained. The probe stage 3 is then used as the ground plane of the MMIC 2a.
Japanese Published Patent Application No. 63-217634 discloses a structure in which part of the probe head including a probing needle adjusting mechanism is covered by an electromagnetic shielding member. The structure in this publication aims at preventing the electronic circuit from being affected by external noise. In this construction, however, an electromagnetic field distribution equivalent to that in a packaged state cannot be realized in the on-wafer state, still leaving the above described problem unsolved.
The prior art microwave band probing apparatus is constructed as described above, and even when the microwave characteristics of the same MMIC are measured, the ground planes of the elements during the measurement in an on-wafer state and at the measurement in a packaged state are different. This makes in the states of the electromagnetic fields different from each other, resulting in differences in the impedances at the measurements, thereby resulting in differences in the microwave characteristics obtained from the measurements.